Error when python program reads a file from an Azure fileshare: "Signature did not match. String to sign used was r..."

Question

I have written the following Python code to generate a SAS token for a file placed in an Azure file share directory:

def getParcelFilePath(webcountyval):
    filePath = rf"/plan/IN/{webcountyval}%20parcels.dbf"
    file_sas_token = generate_file_sas(
       account_name=os.environ["AZURE_STORAGE_ACCOUNT_NAME"],
       account_key=os.environ["AZURE_STORAGE_ACCOUNT_KEY"],
       share_name="dev",
       file_path=filePath,
       permission=AccountSasPermissions(read=True),
       expiry=datetime.datetime.now() + datetime.timedelta(hours=8),
       start=datetime.datetime.now()
     )

     filePathWithToken = os.environ["AZURE_STORAGE_SHARE_URL"] + filePath + "?" + file_sas_token
     return(filePathWithToken)

I live in the Central time zone. To ensure that the authentication does not fail, you can see that I have passed 8 hours to the timedelta() function.

The following URL is generated for the file: https://crestlinecapitalstorage.file.core.windows.net/dev/plan/IN/elkhart%20parcels.dbf?st=2024-11-11T23%3A14%3A30Z&se=2024-11-12T07%3A14%3A30Z&sp=r&sv=2024-11-04&sr=f&sig=[redacted_sig]

When I paste this URL into the browser, it shows the following error: Signature did not match. String to sign used was r 2024-11-11T23:14:30Z 2024-11-12T07:14:30Z /file/crestlinecapitalstorage/dev/plan/IN/elkhart parcels.dbf 2024-11-04

What could be the reason for the error?

Are you sure the account name and key is correct? and what about the file path? Also if I recall correctly the start and expiry times should be in UTC without timezone — Lars Kakavandi-Nielsen
– Lars Kakavandi-Nielsen, Commented Nov 12, 2024 at 6:48
@LarsKakavandi-Nielsen - Yes, I have verified that the account name is correct. I copied the account key from the Azure portal. I even removed the time zone parameter from the datetime function call, and yet the error persists. This thing is a nightmare to get working. — anilcreates
– anilcreates, Commented Nov 12, 2024 at 16:31

anilcreates · Accepted Answer · 2024-11-14 03:00:57Z

It is quite possible that the file_path value “/plan/in/{webcountyval}%20parcels.dbf” was incorrect. The extra ‘/’ at the beginning may not be needed. Anyway, instead of spending any more nightmarish moments trying to get the URL with a SAS token to work, I found a workaround, which is easier to work with and maintain (see AI Overview provided by Google search).

Here's the final code:

def getFileClient(stateval, webcountyval):
    filePath = rf"plan/{stateval}/{webcountyval} parcels.dbf"
    accountKey = os.environ["AZURE_STORAGE_ACCOUNT_KEY"]
    shareName = "dev"

    # Create a ShareClient object
    shareClient = ShareClient(
        account_url=os.environ["AZURE_STORAGE_ACCOUNT_URL"],
        credential=accountKey,
        share_name=shareName
    )

    # Get a reference to the file
    fileClient = shareClient.get_file_client(filePath)
    return(fileClient)

def parcelDBFDataSave(parcelFileClient):

  # Download the file
  fileContent = parcelFileClient.download_file().readall()
  with tempfile.NamedTemporaryFile(delete=False) as tempParcelFile:
    tempParcelFile.write(fileContent)
    tempParcelFileName = tempParcelFile.name

  # Read the first five records 
  with DBF(tempParcelFileName) as dbfRecords:
    i = 0
    for record in dbfRecords:
        logging.info(record)
        i += 1
        if i > 5: break

  return(SUCCESS)

ccParcelFileClient = getFileClient(stateabbr, webCounty)
result = parcelDBFDataSave(ccParcelFileClient)

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